我使用Sqlitebrowser手动创建了一个数据库，其中包含一个Table1表，其中包含5列CellID，纬度，经度，地址和城市。然后我使用以下类来访问数据库：
package com.example.sampledbapp;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper{
//The Android's default system path of your application database.
private static String DB_PATH = "/data/data/com.example.sampledbapp/databases/";
private static String DB_NAME = "sampleDb.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
this.myContext = context;
}
/**
* Creates a empty database on the system and rewrites it with your own database.
* */
public void createDataBase() throws IOException{
boolean dbExist = checkDataBase();
if(dbExist){
//do nothing - database already exist
}else{
//By calling this method and empty database will be created into the default system path
//of your application so we are gonna be able to overwrite that database with our database.
this.getReadableDatabase();
try {
copyDataBase();
} catch (IOException e) {
throw new Error("Error copying database");
}
}
}
/**
* Check if the database already exist to avoid re-copying the file each time you open the application.
* @return true if it exists, false if it doesn't
*/
private boolean checkDataBase(){
SQLiteDatabase checkDB = null;
try{
String myPath = DB_PATH + DB_NAME;
checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}catch(SQLiteException e){
//database does't exist yet.
}
if(checkDB != null){
checkDB.close();
}
return checkDB != null ? true : false;
}
/**
* Copies your database from your local assets-folder to the just created empty database in the
* system folder, from where it can be accessed and handled.
* This is done by transfering bytestream.
* */
private void copyDataBase() throws IOException{
//Open your local db as the input stream
InputStream myInput = myContext.getAssets().open(DB_NAME);
// Path to the just created empty db
String outFileName = DB_PATH + DB_NAME;
//Open the empty db as the output stream
OutputStream myOutput = new FileOutputStream(outFileName);
//transfer bytes from the inputfile to the outputfile
byte[] buffer = new byte[1024];
int length;
while ((length = myInput.read(buffer))>0){
myOutput.write(buffer, 0, length);
}
//Close the streams
myOutput.flush();
myOutput.close();
myInput.close();
}
public void openDataBase() throws SQLException{
//Open the database
String myPath = DB_PATH + DB_NAME;
myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
// Add your public helper methods to access and get content from the database.
// You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
// to you to create adapters for your views.
}
我有一个名为find的按钮，我在其上执行以下代码：
public void btn_Click(View arg){
DatabaseHelper myDbHelper;
myDbHelper = new DatabaseHelper(this);
try {
myDbHelper.createDataBase();
} catch (IOException ioe) {
throw new Error("Unable to create database");
}
try {
myDbHelper.openDataBase();
SQLiteDatabase db = myDbHelper.getReadableDatabase();
String selectQuery = "select CellID from Table1 where _id='2'";
Cursor cursor = db.rawQuery(selectQuery, null);
cursor.close();
Toast.makeText(getApplicationContext(), ""+cursor.getInt(0), Toast.LENGTH_LONG).show();
}catch(SQLException sqle){
throw sqle;
}
}
我收到以下错误：
01-15 17:23:09.834: E/AndroidRuntime(2372): Caused by: android.database.sqlite.SQLiteException: no such table: Table1 (code 1): , while compiling: select CellID from Table1 where _id='2'
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteConnection.nativePrepareStatement(Native Method)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteConnection.acquirePreparedStatement(SQLiteConnection.java:882)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteConnection.prepare(SQLiteConnection.java:493)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteSession.prepare(SQLiteSession.java:588)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteProgram.<init>(SQLiteProgram.java:58)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteQuery.<init>(SQLiteQuery.java:37)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteDirectCursorDriver.query(SQLiteDirectCursorDriver.java:44)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteDatabase.rawQueryWithFactory(SQLiteDatabase.java:1314)
01-15 17:23:09.834: E/AndroidRuntime(2372): at android.database.sqlite.SQLiteDatabase.rawQuery(SQLiteDatabase.java:1253)
01-15 17:23:09.834: E/AndroidRuntime(2372): at com.example.sampledbapp.MainActivity.btn_Click(MainActivity.java:49)
01-15 17:23:09.834: E/AndroidRuntime(2372): ... 14 more
请帮助!!
答案 0 :(得分：0)
因此，我将为您提供所需的代码，如下所示：
public class DatabaseHelper extends SQLiteOpenHelper{
private static String DB_NAME = "sampleDb.db";
private SQLiteDatabase myDataBase;
private final Context myContext;
/**
* Constructor
* Takes and keeps a reference of the passed context in order to access to the application assets and resources.
* @param context
*/
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, 1);
myDatabase = getWritableDatabase(); <-- important part
this.myContext = context;
}
@Override
public synchronized void close() {
if(myDataBase != null)
myDataBase.close();
super.close();
}
@Override
public void onCreate(SQLiteDatabase db) {
put in here your Sql to generate your tables inside the database will be called if no
database exists yet on the device
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
this method doesn't needs to be implemented yet
}
public void yourSelectQuery(){
String selectQuery = "select CellID from Table1 where _id=2";
Cursor cursor = db.rawQuery(selectQuery, null);
cursor.moveToFirst();
Toast.makeText(getApplicationContext(), ""+cursor.getInt(0), Toast.LENGTH_LONG).show();
cursor.close();
}
并在另一个班级
public void btn_Click(View arg){
DatabaseHelper myDbHelper;
myDbHelper = new DatabaseHelper(this);
myDbHelper.yourSelectQuery();
}